Balancing selection in wood formation genes of Eucalyptus

Single Nucleotide Polymorphisms shared between species of distant subgenera (trans-subgeneric SNPs) are likely to be of adaptive importance and persist in separate lineages due to balancing selection. DNA was pooled from 30 individuals representing the natural geographical range of each of three species. Amplicon sequencing identified 6,852 SNPs in 34 candidate genes for wood formation. In pairwise comparisons between species representing distant Eucalyptus subgenera separated by 41 to 46 million years of evolution subgenera between 20-23% of SNPs were shared. The primary signatures of balancing selection were high proportions of trans-subgeneric SNPs in exons and promoters, compared to introns and 3’ untranslated regions. Further analysis revealed ten genes with high proportions of trans-subgeneric SNPs and high nucleotide diversities. This demonstrates that balancing selection is abundant in wood formation genes resulting in an unexpectedly large number of trans-subgeneric SNPs being maintained across divergent Eucalyptus subgenera because it resilience to abiotic and biotic stresses.